I have recently moved into a 1900’s granite built flat in aberdeen. These are built with granite walls 500-600mm thick. One corner of the bedroom has damp patches at low level above the skirting boards. A de-humidifer does control this to an extent but not totally. From the outside there is no signs of cracked pointing. Is this damp air internally causing this problem or would this be damp from outside getting through the solid walls. I have put in a new vent to the blocked up chimney next to he damp but this has made no difference.